In the sport of golf, it is desirable for a golfer's swing to be the same when using any golf club in the golfer's set of clubs. This consistency results in consistently straight and predictable distance drives. With a typical set of golf clubs a golfer is required to slightly adapt his swing according to different characteristics of each different club in order to obtain a straight and maximum distance drive with that club. It is desirable, however, that every golf club in a set have characteristics to allow a golfer to keep a consistent swing and obtain the optimum results with each club.
A golf club is effectively a cantilevered beam (a club shaft held rigidly at a hand gripped end) having a mass (a club head) mounted to one end opposite the hand gripped end. The golfer's swing begins with the take away during which the golfer raises the club from addressing the ball to a raised position. The club is then reversed and the club is swung downwardly. At the beginning of a golfer's downward swing, the grip end of the club is first moved by the golfer's hands and the club shaft flexes, momentarily leaving the massive head in place. The shaft flexes in reaction to the angular acceleration of the club head and any momentum from the take away. Golfers want the shaft to have straightened from the flexed position and be moving forward at the point in the swing at which the club head impacts the ball, in order to maximize the velocity of the club head. This maximum head velocity maximizes the energy transferred to the golf ball, contributed by the shaft assisting in driving it as far as possible with that club. Additionally, with the club shaft straight, the angled face of the club head is correctly oriented with respect to the shaft, giving the ball the specified loft for that club.
It is desirable that each of the different clubs in a golfer's set have characteristics that cause the club shafts to be straight at ball impact regardless of the club in the set being swung. By always getting a straight shaft at impact, regardless of the club, each club can be swung identically, giving optimum results and allowing the golfer to perfect his swing and obtain consistent results. The problem with making each golf club in a set have the desired characteristics is in determining the characteristics of each golf club that are to be as desired, understanding the important parts of each golfer's swing, and matching a golf club to a particular golfer's swing.
Numerous patents have been issued for means and methods for determining characteristics of golfers' swings. Hammond, in U.S. Pat. No. 3,945,646, teaches to mount accelerometers at various locations in a golf club. The accelerometers are electrically connected to a data processor which calculates certain position related characteristics of the golf club during a golfer's swing. This invention uses the accelerometers for analyzing the swing of a particular golfer to correct the swing, not for determining characteristics of a golfer and then matching those characteristics to golf clubs.
In U.S. Pat. No. 4,615,526, Yasuda et al. mount magnets and sensors to a golf club and a platform. The apparatus is used during the swing of the club to determine the velocity of the club head and angle of approach at, and near, ball impact. These characteristics of the golfer's swing are also used to analyze a golf swing for the purpose of correction, not to match a golfer to a golf club.
Additional U.S. Pat. Nos. 4,630,829, 4,878,672, 4,967,596, and 4,991,850 teach the use of electrical and mechanical devices for measuring velocity, centrifugal force during club swing, and impact energy of a ball with a club head. Most of these inventions are used to determine characteristics about a golfer's swing in order to correct or change the golfer's swing. None of the prior art inventions use characteristics of a golfer's swing to determine the flexibility a golf club shaft should have for that golfer.
It is known to take a plurality of golf clubs that have different natural frequencies of oscillation and, by trial and error, find the natural frequency of a golf club that best matches a particular golfer. This is done by the golfer taking numerous swings with each golf club, and choosing the one which gives the golfer the best respective results, such as drive distance and straightness of drive.
It is also known to make a chart which tells how much of a golf club shaft to remove from each end of the shaft in order to arrive at the desired natural frequency. In U.S. Pat. No. 4,122,593, Braly discloses a chart which is used to find a desired natural frequency and length in order to determine how much to remove from each end of a golf club shaft.
Additionally, in U.S. Pat. No. 4,555,112, Masghati discloses a golf club shaft having tip and grip ends which always remain the same length, but which have a connecting, central portion having length and wall thickness which can be varied.
The need exists for a method for measuring specific characteristics of a golfer's swing, and matching a golf club or a set of golf clubs to those characteristics. This matching method should include the determination of how much of a shaft should be removed.